1. Technical Field
The present invention relates to a vehicle power assist steering system. In particular, the present invention relates to an electric power assist steering system which includes an electric assist motor for applying force to a steering member, such as a rack.
2. Description of the Prior Art
A known type of vehicle power assist steering system includes a ball nut for transmitting force between a steering member and an electric assist motor. The steering system also includes an electronic control unit, or ECU, for controlling operation of the electric motor. Upon actuation of the electric motor, the ball nut is driven to rotate relative to the steering member. The rotational force of the ball nut is transmitted to the steering member to drive the steering member axially. Axial movement of the steering member effects turning movement of the steerable wheels of the vehicle.
The housing of the assist motor is typically machined from steel. The process of machining the housing is difficult and costly.